The present disclosure generally relates to enhancing images from electronic displays, and specifically to varying the focal length of optics to enhance the images.
A head mounted display (HMD) can be used to simulate virtual environments. Conventional binocular HMDs vary the stimulus to vergence with the information being presented to a viewing user in a virtual scene, while the stimulus to accommodation remains fixed at the apparent distance of the display, as created by the viewing optics. Sustained vergence-accommodation conflict (VAC) has been associated with visual discomfort, motivating numerous proposals for delivering near-correct accommodation cues.
Vergence is the simultaneous movement or rotation of both eyes in opposite directions to obtain or maintain single binocular vision which is connected to accommodation of the eye. Under normal conditions, changing the focus of the eyes to look at an object at a different distance automatically causes vergence and accommodation. For example, as a real object moves closer to a user looking at the real object, the user's eyes rotate inward to stay verged on the object. As the object gets closer to the user, the eyes must “accommodate” for the closer distance by reducing the power or focal length, which is achieved automatically by each eye changing its shape. Thus, under normal conditions in the real world, the vergence depth corresponds to where the user is looking, which also equals the focal length of the user's eyes.
A conflict between vergence and accommodation, however, often occurs with some three-dimensional (3D) electronic displays. For example, as a virtual object is rendered on the 3D electronic display to move closer to a user looking at the object, each of the user's eyes rotates inward to stay verged on the object, but the power or focal length of each eye is not reduced; hence, the user's eyes do not accommodate as in the real-world. Instead of reducing power or focal length to accommodate for the closer vergence depth, the eyes maintain accommodation at a distance associated with 3D electronic display. Thus, the vergence depth often does not equal the focal length for the human eye for objects displayed on 3D electronic displays. This discrepancy between vergence depth and focal length is referred to as “vergence-accommodation conflict.” A user experiencing only vergence or accommodation (and not both simultaneously) can experience some degree of fatigue or nausea, which is undesirable for virtual reality system creators.